1. Field of the Invention
Embodiments of the present invention relate to the demodulation of optical signals. Some example embodiments relate more particularly to the demodulation of phase shift keyed signals.
2. Related Technology
A phase shift keyed (PSK) optical signal typically includes a return-to-zero (RZ) signal having a series of relatively high intensity pulses separated by low intensity regions. For a differential PSK optical signal, the phase difference between adjacent pulses encodes information. For example, in some encoding schemes, a phase difference of it encodes a one bit whereas a phase difference of zero or 2π encodes a zero bit. PSK signals have a distinct advantage in that both the zero bit and the one bit contain the same amount of optical energy, which enables a higher signal-to-noise ratio (SNR) at a demodulator as compared to encoding methods where a logical zero is encoded by a signal portion having a lower intensity than a logical one.
Demodulation of a PSK signal includes converting the phase information encoded in the pulses into amplitude modulation such that the data can be detected by means of a photodiode or other optical sensor. In a conventional demodulator, this is a accomplished by means of a delay line interferometer (“DLI”), such as a Mach-Zehnder interferometer or Michelson interferometer. A DLI operates by dividing an input signal into first and second signals. The first and second signals travel along paths of different lengths and are then rejoined into one or more output signals. The difference in path length is chosen such that upon recombining, the first and second signals will constructively and/or destructively interfere with one another depending on the phase difference between adjacent pulses.
The subject matter claimed herein is not limited to embodiments that solve any disadvantages or that operate only in environments such as those described above. Rather, this background is only provided to illustrate one exemplary technology area where some embodiments described herein may be practiced